The present invention relates generally to waveguide techniques, such as with waveguides in which facing surfaces are approximately parallel and separated by a region that can contain fluid.
U.S. Patent Application Publication No. 2006/0092413 describes anti-resonant waveguide sensors in which light is guided within a medium between a substrate and a covering layer both made from a transparent material such as glass; the transparent material has an index of refraction slightly higher than the medium, which can be a sample such as a thin film of liquid, gas, or aerosol carrying a target analyte. As a result, an anti-resonant wave can be generated in the medium in accordance with eigensolutions of a Helmholtz equation. Each eigensolution can be called an optical mode, and can be excited by directing a beam of light at the waveguide at a specific angle of incidence. The waveguide can have a tilted entrance facet to minimize reflection of an incident beam; other possible geometries include curved end facets and cylindrical sample shapes. A laser, a source of white light, or a light-emitting diode can provide the incident beam, while detectors can detect light propagating through the sample or scattered, refracted, or fluoresced by the sample, such as with wavelength sensitive elements.
Singh, K., Liu, C., Capjack, C., Rosmus, W., and Backhouse, J., “Analysis of cellular structure by light scattering measurements in a new cytometer design based on a liquid-core waveguide”, IEEE Proc.-Nanobiotechnol., Vol. 151, No. 1, February 2004, pp. 10-16, describes a microfluidic optical cytometer used to generate and observe light scattered from biological cells. The cytometer includes a leaky waveguide, and an incoming laser beam can be coupled into the waveguide through a prism at an angle of incidence for a waveguide mode. A waveguide can include a microfluidic channel fabricated on a glass substrate with a glass superstrate, where the liquid microchannel can be a low index waveguide core 10-30 μm deep. One method to form a microchannel structure is to deposit a spin-coated or dip-coated polymer layer on the substrate, about 30 μm thick, and then pattern the layer with desired microchannels, about 1 mm in width. The superstrate is then bonded onto the patterned polymer layer, forming the microchannel waveguide structure. The polymer layer serves to separate the two glass slides, and is not illuminated; photoresist is particularly useful as the polymer layer. Images of scattered light can be taken using an optical microscope and a CCD camera, either to view an image of a cell or to obtain its characteristic scattering pattern.
It would be advantageous to have improved waveguide techniques.